Pressure sensor, e.g. in sole for an article of footwear

ABSTRACT

A pressure sensor, e.g. for being arranged in the sole structure of an article of footwear, for measuring a pressure exerted by the wearer&#39;s foot. The pressure sensor has one or more pressure-sensing cells. Each cell has a first flexible carrier film and a second flexible carrier film, the first and second carrier films being attached to one another by a spacer film having an opening, a plurality of first electrodes arranged on the first carrier film and a plurality of second electrodes arranged on the second carrier film. The plurality of first electrodes has a first group of electrodes and a second group of electrodes. The first and second groups of electrodes are arranged so as to interdigitate with delimiting gaps there between. One or more electrically insulating overprints are arranged on the first carrier film so as to cover the gaps.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/406,193 filed on Dec. 5, 2014, which is a United States nationalphase of International Patent Application No. PCT/EP2013/061665 filedJun. 6, 2013, which claims priority to Luxembourg Application No. 92 016filed Jun. 6, 2012, the disclosures of which are all hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

The present invention generally relates to a pressure sensor, especiallybut not exclusively for an article of footwear, such as e.g. a shoe, aboot, a sandal or the like. Such a pressure sensor may be used formeasuring pressure exerted by the wearer's foot on the sole structure.

BACKGROUND ART

Document US 2010/0063779 discloses a shoe with an integrated sensorsystem. The sensor system collects performance data that are transferredfor further use via a communication port. The shoe contains a forcesensor arranged in the sole structure for measuring, in a plurality ofareas, pressure (force) exerted by the wearer's foot on the solestructure, and an electronic module configured to gather data from thesensors. The module is configured for transmitting the data to anexternal device for further processing. In one of the embodimentsdisclosed in US 2010/0063779, the pressure sensor comprises fourelongated pressure-sensing cells, each of which contains a first and asecond electrode as well as a force-sensitive resistive materialdisposed between the electrodes to electrically connect the electrodestogether. When pressure is applied to the force-sensitive material, itsresistivity changes, and the resulting change in resistance is detectedby the electronic module. Materials exhibiting volume-based resistancebehavior are used as the force-sensitive material: when such material iscompressed, conductive particles contained therein move closer together,whereby conductive paths are formed and the resistance decreases. Ifanother resistance vs. pressure characteristic is needed, a suitableforce-sensitive material has to be found, which may be difficult.

BRIEF SUMMARY

The invention provides a pressure sensor, wherein the one or morepressure sensing cells have an increased dynamic range, i.e. whoseelectrical resistance decreases more slowly with increasing pressure butover a broader range.

The proposed pressure sensor comprises one or more pressure-sensingcells. Each cell comprises a first flexible carrier film and a secondflexible carrier film, the first and second carrier films being attachedto one another by a spacer film having an opening, a plurality of firstelectrodes arranged on the first carrier film and a plurality of secondelectrodes arranged on the second carrier film, the plurality of firstelectrodes and the plurality second electrodes being arranged in facingrelationship with each other in the opening in such a way that the firstand second electrodes may be brought into contact with one another whenpressure is exerted on the pressure-sensing cell and that contact areasbetween the first and second electrodes increase with increasingpressure. The first electrodes are resistive electrodes (e.g. made ofgraphite ink, carbon ink, graphite-carbon ink or the like). Theplurality of first electrodes comprises a first group of electrodes anda second group of electrodes, the first and second groups of electrodesbeing arranged so as to interdigitate while delimiting gaps therebetween. The first carrier film carries conductive tracks that contactborder portions of the first electrodes, which extend along the gaps,each conductive track defining an equipotential line in the respectiveborder portion. One or more electrically insulating overprints arearranged on the first carrier film so as to cover the gaps. Theoverprints at least partially overlap with (preferably completely cover)the border portions in which the first electrodes are contacted by theconductive tracks. The electrically insulating overprints locallyprevent a direct contact between the first and second electrodes andenable the direct contact where they are absent. The pressure sensoraccording to the invention may especially (but not exclusively) be usedin an article of footwear (in particular a sports shoe, such as e.g. arunning shoe, a tennis shoe or the like) that comprises a sole structurefor supporting a wearer's foot and an upper for holding the wearer'sfoot onto the sole structure. In this case, a pressure sensor accordingto the invention is preferably arranged in the sole structure formeasuring a pressure exerted by the wearer's foot on the sole structure.

The above-described pressure-sensing cell exhibits an improved dynamicresponse due to the presence of the electrically insulating overprintsand the conductive tracks in the border regions of the first electrodes.These layers locally reinforce the first carrier film, whereby themechanical response of the carrier film is shifted to higher pressures(i.e. it bends less easily under pressure). It follows that the rate ofgrowth of the contact area between the first and second electrodesdecreases with increasing pressure (at higher pressures, the contactarea spreads towards the borders of the pressure-sensitive cell, whereat least the first carrier film yields less easily under pressure due tothe presence of the conductive track and the overprints). This means, inturn, that maximum mechanical contact between the first electrodes andthe second electrodes occurs at a higher pressure than in conventionalpressure sensing cells.

Preferably, the pressure-sensing cells are configured (in particular bytailoring of the shape of the electrically insulating overprints) insuch a way that pressures in the range from about 0.1 bar to 7 bartranslate into a steady change of the contact area between the resistiveelectrodes (and thus of the electrical resistance of the cell) from 0%(at the turn-on pressure, i.e. at the about 0.1 bar) and about 100%(full contact at about 7 bar).

Preferably, also the second electrodes are resistive electrodes.Alternatively, they can be conductive electrodes (e.g. made of a silverink or a conductive carbon/graphite ink). The electrically insulatingoverprints are preferably made of electrically insulating (dielectric)ink.

Advantageously, the plurality of second electrodes comprises a thirdgroup of electrodes and a fourth group of electrodes, the third andsecond fourth groups of electrodes being arranged so as to interdigitatewhile delimiting gaps there between. Most preferably, the first andsecond electrodes are mirror-symmetrical to each other.

Also the second carrier film may carry conductive tracks that contactborder portions of the second electrodes extending along the gaps.

The third and fourth groups of electrodes may be separated from eachother by a high impedance when the first and second electrodes are notin contact with one another and shunted via the first electrodes whenthe first and second electrodes are in contact with one another.Additionally or alternatively, the first and second groups of electrodesmay be separated from each other by a high impedance when the first andsecond electrodes are not in contact with one another and shunted viathe second electrodes when the first and second electrodes are incontact with one another.

Preferably, the one or more sensor cells of a pressure sensor to bearranged in a sole structure of an article of footwear are located inareas expected to be subjected to pressure peaks when the wearer of thefootwear is standing still, is walking or is running. Advantageously,each of the one or more sensor cells is preferably located in an areacorresponding to a bone or part of bone of a wearer's foot selected fromthe heel bone, the head of the first metatarsal bone, the head of thefourth or fifth metatarsal bone, the head of the second or thirdmetatarsal bone and the head of the first phalange. Those skilled willappreciate that pressure maxima are typically located under the heelbone, under the heads of the fourth and/or fifth metatarsal bone andunder the head of the first phalange when the wearer is standing atrest; when the wearer is walking, the pressure maxima are usually underthe heel bone, under the heads of the second and/or third metatarsalbone and under the head of the first phalange.

The pressure-sensing cells may have various shapes. For instance, eachof the pressure-sensing cells may be oval, elliptical or rectangularwith rounded angles.

For equalization of gas pressure inside the opening, each of thepressure sensing cells advantageously comprises a ventilation hole. Theventilation hole may be in fluid communication with the exterior of thepressure sensor (e.g. the atmosphere) or with a gas (e.g. air) reservoirwithin the pressure sensor. Such gas reservoir could e.g. be a cavitybetween the first and second carrier films.

According to a preferred embodiment of the invention, the pressuresensor comprises a foam rubber support, e.g. made of ethylene vinylacetate (EVA), preferably fixed to the first or the second carrier filmby means of an adhesive.

As those skilled will appreciate, the pressure sensor could be arrangedin different parts of a sole structure of footwear. For instance, thepressure sensor could be arranged on or in the insole. Alternatively,the pressure sensor could be arranged on, in or under the midsole.

Another aspect of the present invention relates to a pressure sensor foran article of footwear that comprises a flexible multilayer filmstructure, wherein the pressure sensor further comprises a trough-shapedreceptacle for an electronic control module, the receptacle comprisingin its interior a plurality of connection pins for interfacing thepressure sensor with the electronic control module. Preferably, thetrough-shaped receptacle is made of plastic material, e.g. PET or epoxy.

The receptacle is preferably arranged in an opening provided in theflexible multilayer film structure. The receptacle may comprise a bottompart and a top part, the bottom part and the top part being assembledwith each other so as to squeeze between each other a border of theopening in the multilayer film structure and thus securing themultilayer film structure to the receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred, non-limiting, embodiments of the invention will now bedescribed, by way of example, with reference to the accompanyingdrawings in which:

FIG. 1 is a longitudinal cross sectional view of the sole structure of asports shoe equipped with a pressure sensor in accordance with apreferred embodiment of the invention;

FIG. 2 is a top view of the pressure sensor of the sports shoe of FIG.1;

FIG. 3 is an exploded view of one of the pressure-sensing cells of thepressure sensor of FIG. 2;

FIG. 4 is a schematic cross sectional view of the B-B plane of FIG. 3;

FIG. 5 is a graph illustrating the difference in the electricalresponses of a pressure-sensing cell without an electrically insulatingoverprints and one with such overprints;

FIG. 6 is a block diagram of the electrical circuit of the pressuresensor illustrated in FIG. 2;

FIG. 7 is a schematic block diagram of an alternative electrical circuitfor the pressure sensor of FIG. 2;

FIG. 8 is a schematic block diagram of another alternative electricalcircuit for the pressure sensor of FIG. 2;

FIG. 9 is an exploded view of a variant of the pressure-sensing cell ofFIG. 3;

FIG. 10 is an illustration of the pressure-dependent growth of thecontact areas between the electrodes of a pressure-sensing cell as shownin FIG. 3 or 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

An article of footwear, in form of a sports shoe 10 is depicted in FIG.1 as including an upper 12 and a sole structure 14. The upper 12 issecured to sole structure 14 and defines a chamber for receiving a foot.The sole structure 14 includes an outsole 14.1, a midsole 14.2, and aninsole 14.3, which forms the bottom of the foot-receiving chamber of thesport shoe 10.

The film-type pressure sensor is arranged on the upper surface of an EVAsubstrate 17. In the illustrated embodiment, the midsole 14.2, which ispreferably formed of impact-attenuating material, has the film-typepressure sensor 16 on its substrate 17 attached to its upper surface.When the insole is in place, the pressure sensor 10 is thus sandwichedbetween the insole 14.3 and the midsole 14.2.

As best shown in FIG. 2, the pressure sensor 16 comprises a plurality ofpressure-sensing cells 18, located in different areas of the solestructure 14, for measuring pressure exerted by the wearer's foot on thesole structure 14.

The configuration of the pressure sensing cells 18 will now be describedwith reference to FIGS. 3 and 4. FIG. 3 shows the different layers of apressure-sensing cell 18. FIG. 4 shows the pressure-sensing cell of FIG.3 in cross section. The pressure sensor 16 comprises a multilayeredstructure including a first carrier film 20, a second carrier film 22,and a spacer 24. The spacer 24 is typically a double-sided adhesive,with which the first and second carrier films 20, 22 are laminatedtogether. The first and second carrier films 20, 22 are preferably madeof PET but other materials such as PEN, PI, PEEK etc. are also possible.Each of the carrier films may consist of a single film layer or comprisea plurality of film layers of the same or different materials. Thespacer 24 preferably comprises a PET, PEN, PI, PEEK, etc. film layerwith an adhesive coating applied on each side thereof. At eachpressure-sensing cell 18, the spacer comprises an oblong opening 26,within which the first and second carrier films 20, 22 may be pressedtogether. In each pressure-sensing cell 18, a plurality of first,resistive, electrodes 28 is printed on the first carrier film 20 and aplurality of second electrodes 30 is printed on the second carrier film22, in facing relationship with the a plurality of first electrodes 28.Each plurality of electrodes 28, 30 is contacted by a respectiveconductive track 34, 36. The plurality of first electrodes 28 ispartially covered with electrically insulating overprints 32 (made e.g.of a dielectric ink), in such a way as to locally prevent a directcontact between the electrodes on the first carrier film 20 and those onthe second carrier film 22.

As best illustrated in FIG. 3, the plurality of first electrodes 28comprises a first group of electrodes and a second group of electrodesarranged so as to interdigitate while delimiting gaps 42 there between.The electrodes of each group contact the conductive track 34 only on onelongitudinal side of the pressure-sensitive cell 18. The conductivetrack 34 comprises studs 35 arranged in contact with border portions ofthe first electrodes 28 that extend along the gaps 42. Likewise, theplurality of second electrodes 30 comprises a third group of electrodesand a second group of electrodes arranged so as to interdigitate whiledelimiting gaps 42′ there between. The electrodes of each group contactthe conductive track 36 only on one longitudinal side of thepressure-sensitive cell 18. The conductive track 36 comprises studs 35′arranged in contact with border portions of the second electrodes 30that extend along the gaps 42′.

In response to pressure acting on the pressure-sensing cell 18, at leastone of the first and second carrier films 20, 22, deflects towards theother carrier film until the carrier films 20, 22 or the elements ontheir respective surface come into contact. FIG. 10 illustrates theevolution of the mechanical contact areas on the second carrier film 22.Contours 64, 64′ and 64″ represent the contact areas as pressure on thepressure-sensing cell increases. Once contact is established (innercontours 64), the radius of the mechanical contact areas increases (seearrows 66) with increasing pressure. When a direct contact isestablished between the electrodes 28 and 30, the electrical resistancebetween the conductors 34 and 36 becomes finite and a current may flowin consequence. As the contact area between the first and secondelectrodes 28, 30 increases, the resistance measurable between theconductors 34 and 36 decreases. The positions of the contacts betweenthe resistive electrodes 28, 30 and the respective conductive trace 34,36, the specific resistance of the resistive electrodes, the shape ofthe first and second electrodes 28, 30, the shape of the electricallyinsulating overprints 32 and the mechanical properties of the carrierfilms 20, 22 determine the pressure-dependent cell resistance. Referringto the cell configuration of FIGS. 3, 9 and 10, the first and secondelectrodes 28, 30 have a roughly equal-sided triangular shape. The baseof the triangles extends substantially parallel to the longitudinal axisof the pressure-sensing cell. Each electrode 28, 30 is contacted withthe conductive studs 35, 35′ at the tip opposite the base. The initialcontact (contours 64) between the first and second electrodes 28, 30occurs approximately at the center of each triangle. The dielectricoverprints 32 on the first electrodes 28 (shown as a dashed line in FIG.10) prevent that a single, continuous contact area is formed. Eachcontact area grows as roughly shown by arrows 66 when pressureincreases. When the contact area has reached a certain size, theresidual resistance between the conductors 34 and 36 is mainly due tothe resistive path between the contact areas and the conductive studs35, 35′. (The resistance of the conductive tracks and the studs may beneglected.) At higher pressures, each contact area grows into the regionbetween the studs 35, 35′, which tapers in the direction of the tip ofthe triangle. Since the dielectric overprints 32 locally maintain thecarrier films 20, 22 at a certain minimum distance from each other, therate of growth of the contact area decreases as the contact area entersthe region between the studs 35, 35′.

The electrical response function of the pressure-sensing cells, i.e. theresistance versus pressure, may be adjusted in a predetermined manner bysuitably shaping the overprints 32, because the electrically overprints32 locally prevent a direct contact between the first and secondelectrodes 28, 30 whereas the direct contact is possible in those areaswhere the electrically insulating overprints 32 are absent.

FIG. 5 schematically illustrates the difference in the electricalresponse of a pressure-sensing cell without the overprints (dotted curve38) and one with the overprints shaped as in FIG. 3 (continuous curve40), all other cell parameters being the same. One notes that for thepressure-sensing cell without the insulating overprints the resistancechange occurs in a relatively small pressure range starting at theactivation pressure p_(act) (the pressure at which the electrodes enterinto contact). Above p_(act), the resistance quickly levels out at a lowvalue. For the cell equipped with the insulating overprints, theresistance change spreads over a significantly longer pressure interval.As a consequence, the cell with the insulating overprints enablespressure measurement at significantly higher pressures than the cellwithout the insulating overprints. It shall be noted that the conductivestuds 35, 35′ and the insulating overprints 32 also locally reinforcethe carrier films 20, 22. The suppleness of the carrier films 20, 22 isthus locally reduced, which means that, in vicinity of the conductivestuds and the insulating overprints, more pressure is needed to bringthe first and second electrodes into contact, which increases thedynamic range of the sensor.

As best illustrated in FIG. 2, the pressure-sensing cells 18 arearranged in areas of the shoe 10, in which the pressure peaks areexpected to occur when the wearer is standing, walking or running.Specifically, a first one of the pressure-sensing cells is positioned inthe area of the head of the first phalange (big toe), a second one inthe area of the head of the first metatarsal bone, a third one in thearea of the head of the fifth metatarsal bone and a fourth one in thearea of the calcaneum (heel bone).

For fixation of the pressure sensor 16 to the sole structure 14 (in thisexample the midsole), the pressure sensor 16 comprises one or morefixation pads 44 (see FIG. 2). The fixation pads 44 preferably comprisea layer of pressure-sensitive or heat-activatable adhesive, initiallyprotected by a release liner, which is removed just before the pressuresensor 16 is attached to its carrier member of the sole structure 14.Instead of using local fixation pads 44, the entire surface of the first20 or the second 22 carrier film can be coated with an adhesive (andinitially protected by a release liner).

The pressure sensor 16 further comprises an electronic control module46, which is arranged within a trough-shaped receptacle 62 andmechanically attached to the multilayer film structure of thepressure-sensor 10. Connection strips 48 interconnect the pressuresensing cells 18 and the electronic control module 46. The connectionstrips 48 are integral part of the multilayer film structure of thepressure sensor 16 and carry conductive tracks that electrically connectthe first and second electrodes of each pressure-sensing cell 18 withthe electronic control module 46. The connection strips 48 may have aserpentine shape to act as springs and to thereby increase thepressure-sensor's elasticity in the sensor plane.

The electronic control module 46 preferably comprises anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), a microprocessor, or the like. Advantageously, theelectronic control circuit is configured for wirelessly transmitting thecollected pressure data or any data derived there from to a receiverappliance having a user interface. Such receiver appliance could includea (wrist-) watch, the wrist receiver of a heart rate monitor, a handheldcomputer, a mobile phone, a portable media player or the like. In theillustrated embodiment, the electronic control module 46 is arranged ina cavity or well of the midsole 14.2. The cavity or well may be locatedelsewhere in the sole structure 14 in other embodiments.

For equalization of gas pressure inside the opening 26 of the spacer 24,each pressure-sensing cell 18 comprises a ventilation hole 58 (bestshown in FIGS. 2 and 3). The ventilation holes 58 fluidly connect theinteriors of the pressure sensing cells to the outside, so thatcompression of the gas inside the pressure sensing cells is essentiallyavoided and thus has no significant impact on the response curve of eachcell 18. Additionally, or alternatively, the ventilation holes 58 couldbe connected to a gas reservoir within the film-type pressure sensor.

FIG. 6 is a schematic block diagram of the flexible circuit of thepressure sensor 16. The pressure-sensing cells 18 are drawn as variableresistors 18.1-18.4. The cells are arranged electrically in parallelbetween a respective terminal 50.1, 50.2, 50.3 or 50.4 of the electroniccontrol module (not shown in FIG. 6) and circuit ground 52. Theelectronic control module determines the pressure values based upon theresistance (or the current or the voltage if one of these quantities iskept constant) measured between each terminal 50.1, 50.2, 50.3 or 50.4and circuit ground. It should be noted that the cell response curve isinfluenced by changes in resistivity of the electrode material, whichmay vary depending on ageing, temperature, humidity or otherenvironmental influences. To be able to correct or compensate suchinfluence on the pressure values, a reference resistor 54 is provided.The reference resistor 54 is made of the same material as the electrodes28, 30. It is arranged somewhere on the pressure sensor 16 so that itexperiences essentially the same environmental influences as theelectrodes 28, 30. In the illustrated embodiment, the reference resistor54 is arranged electrically between a reference terminal 56 and circuitground 52, in parallel to the pressure sensing cells. The electroniccontrol module measures the resistance of the reference resistor 54. Anydeviation from a nominal value is used to correct the readings of thepressure-sensing cells 18. The reference resistor 54 may be arranged oneither one of the carrier films 20, 22. One could also use a pluralityof resistors arranged on one or both of the carrier films. Anotherpossibility would be to provide a preloaded pressure-sensing cell (i.e.a pressure-sensing cell wherein the electrodes are permanently kept incontact).

The reference resistor 54 and the resistive electrodes 28, 30 of thepressure-sensing cells are preferably obtained by printing of carbon inkon the respective carrier film. The conductive tracks 34, 36 (includingstuds 35 and 35′) are preferably made of silver ink.

FIG. 7 is a schematic block diagram of an alternative flexible circuitfor the pressure sensor 16. Unlike in the flexible circuit of FIG. 6,the reference resistor 54 is arranged electrically between circuitground 52 and the pressure-sensing cells 18, drawn again as variableresistors 18.1-18.4, in the manner of a voltage divider. During themeasurement, one pressure-sensing cell at a time may be connected to avoltage source (e.g. a battery) by means of its terminal 50.1, 50.2,50.3 or 50.4. The electronic control module determines the pressurevalues based upon the voltages measured on measurement terminal 60. Theresistance R_(X) of one of the pressure-sensing cells 18.1-18.4 may beobtained by R_(x)=R_(ref)(U₀/U_(meas)−1), where R_(ref) is theresistance of the reference resistor, U₀ the voltage applied at theterminal 50.1, 50.2, 50.3 or 50.4, and U_(meas) the voltage measured atthe terminal 60. As one supposes that the resistances of thepressure-sensing cells and the reference resistors are subjected to thesame changes due to environmental influences (temperature, ageing,etc.), the normalized resistance R_(x)/R_(ref) is essentiallyindependent of these effects. In all other respects, the circuit for thepressure sensor 16 of FIG. 7 is configured and operates in the same wayas the one of FIG. 6.

FIG. 8 is a schematic block diagram of another alternative flexiblecircuit for the pressure sensor 16. According to this alternative, thereference resistor 54 is arranged in parallel with one of thepressure-sensing cells 18.1-18.4. In this arrangement, the referenceresistance is substantially higher than the resistances of thepressure-sensing cells 18.1-18.4 in actuated state (i.e. above theactivation pressure).

FIG. 9 shows a variant of the pressure-sensitive cell 18 of FIG. 3. Theonly difference with respect to FIG. 3 is that the third and fourthgroups of second electrodes 30 are contacted by separate conductivetracks 36, 36′. The third and fourth groups of electrodes are thusseparated from each other by a high impedance when the first and secondelectrodes are not in contact with one another. They are shunted via thefirst electrodes when the first and second electrodes are in contactwith one another. The electrical resistance of the cell is measuredbetween the conductive tracks 36 and 36′. The pressure-sensitive cellis, therefore, of the so-called “shunt-mode” type. (In contrast, thecell of FIG. 3 is said to be of the “through-mode” type; the electricalresistance is measured between the conductive traces 34 and 36). Thefirst carrier film 20 may also carry separate conductive tracks thatcontact border portions of the first electrodes 28 extending along thegaps, each of the conductive tracks defining an equipotential line, andwherein one or more electrically insulating overprints are arranged onthe first carrier film 20 so as to cover the gaps. The overprints atleast partially overlap with the border portions in which the firstelectrodes are contacted by the conductive tracks.

While specific embodiments have been described in detail, those withordinary skill in the art will appreciate that various modifications andalternatives to those details could be developed in light of the overallteachings of the disclosure. Accordingly, the particular arrangementsdisclosed are meant to be illustrative only and not limiting as to thescope of the invention, which is to be given the full breadth of theappended claims and any and all equivalents thereof.

1. A pressure sensor comprising one or more pressure-sensing cells, eachof said pressure sensing cells comprising: a first flexible carrier filmand a second flexible carrier film, said first and second carrier filmsbeing attached to one another by a spacer film having an opening; and aplurality of first electrodes arranged on said first carrier film and aplurality of second electrodes arranged on said second carrier film,said plurality of first electrodes and said plurality second electrodesbeing arranged in facing relationship with each other in said opening insuch a way that said first and second electrodes may be brought intocontact with one another when pressure is exerted on saidpressure-sensing cell and that contact areas between said first andsecond electrodes increase with increasing pressure, wherein said firstelectrodes are resistive electrodes, wherein said plurality of firstelectrodes comprises a first group of electrodes and a second group ofelectrodes, said first and second groups of electrodes being arranged soas to interdigitate while delimiting gaps there between, wherein saidfirst carrier film carries conductive tracks that contact borderportions of said first electrodes extending along said gaps, eachconductive track defining an equipotential line, and wherein one or moreelectrically insulating overprints are arranged on said first carrierfilm so as to cover said gaps, said overprints at least partiallyoverlapping with the border portions in which said first electrodes arecontacted by said conductive tracks.
 2. The pressure sensor as claimedin claim 1, wherein said second electrodes are resistive electrodes. 3.The pressure sensor as claimed in claim 1, wherein said plurality ofsecond electrodes comprises a third group of electrodes and a fourthgroup of electrodes, said third and second fourth groups of electrodesbeing arranged so as to interdigitate while delimiting gaps therebetween.
 4. The pressure sensor as claimed in claim 3, wherein saidsecond carrier film carries conductive tracks that contact borderportions of said second electrodes extending along said gaps.
 5. Thepressure sensor as claimed in claim 3, wherein said third and fourthgroups of electrodes are separated from each other by a high impedancewhen said first and second electrodes are not in contact with oneanother and wherein said third and fourth groups of electrodes areshunted via said first electrodes when said first and second electrodesare in contact with one another.
 6. The pressure sensor as claimed inclaim 4, wherein said third and fourth groups of electrodes areseparated from each other by a high impedance when said first and secondelectrodes are not in contact with one another and wherein said thirdand fourth groups of electrodes are shunted via said first electrodeswhen said first and second electrodes are in contact with one another.7. The pressure sensor as claimed in claim 1, wherein said first andsecond groups of electrodes are separated from each other by a highimpedance when said first and second electrodes are not in contact withone another and wherein said first and second groups of electrodes areshunted via said second electrodes when said first and second electrodesare in contact with one another.
 8. The pressure sensor as claimed inclaim 1, said pressure sensor being configured for being arranged in asole structure of an article of footwear in order to measure a pressureexerted by a wearer's foot on the sole structure, wherein said one ormore sensor cells are located in areas expected to be subjected topressure peaks when the wearer is standing still, is walking or isrunning.
 9. The pressure sensor as claimed in claim 8, wherein each ofsaid one or more sensor cells is located in an area corresponding to abone or part of bone of a wearer's foot selected from the heel bone, thehead of the first metatarsal bone, the head of the fourth or fifthmetatarsal bone, the head of the second or third metatarsal bone and thehead of the first phalange.
 10. The pressure sensor as claimed in claim1, wherein each of said pressure sensing cells is oval, elliptical orrectangular with rounded angles.
 11. The pressure sensor as claimed inclaim 1, wherein each of said pressure sensing cells comprises aventilation hole for equalization of gas pressure inside said opening.12. The pressure sensor as claimed in claim 11, wherein said ventilationhole is in communication with an exterior or a gas reservoir.
 13. Thepressure sensor as claimed in claim 1, comprising a foam rubber support.14. The pressure sensor as claimed in claim 13, wherein said foam rubbersupport is made of ethylene vinyl acetate.
 15. The pressure sensor asclaimed in claim 1, wherein said first electrodes have generally theshape of an equal-sided triangle and wherein said conductive tracks thatcontact border portions of said first electrodes comprise studsextending from a tip of said triangle.
 16. The pressure sensor asclaimed in claim 1, wherein said second electrodes have generally theshape of an equal-sided triangle and wherein said conductive tracks thatcontact border portions of said second electrodes comprise studsextending from a tip of said triangle.
 17. A pressure sensor preferablyas claimed in claim 1, comprising a flexible multilayer film structure,wherein the pressure sensor further comprises a trough-shaped receptaclefor an electronic control module, said receptacle comprising in itsinterior a plurality of connection pins for interfacing said pressuresensor with said electronic control module.
 18. The pressure sensor asclaimed in claim 17, wherein said receptacle is arranged in an openingprovided in said flexible multilayer film structure.
 19. The pressuresensor as claimed in claim 17, wherein said receptacle comprises abottom part and a top part, said bottom part and said top part beingassembled with each other so as to squeeze between each other a borderof said opening in said multilayer film structure and thus securing saidmultilayer film structure to said receptacle.
 20. The pressure sensor asclaimed in claim 18, wherein said receptacle comprises a bottom part anda top part, said bottom part and said top part being assembled with eachother so as to squeeze between each other a border of said opening insaid multilayer film structure and thus securing said multilayer filmstructure to said receptacle.